1. Field of the Invention
The present invention relates to an automotive safety device which, upon the onset of a collision, deploys an inflatable restraint cushion, commonly known as an air bag, so as to provide impact protection to occupants of the passenger vehicles. More particularly, this invention relates to an improved device for securing an air bag cushion to a canister.
2. Description of Related Art
An air bag restraint system typically includes a canister, which has an open side and which canister encloses an inflator and at least part of an air bag, and a cover which conceals the module from view. A driver side air bag module is typically mounted in the center of the steering wheel behind a protective cover. When the air bag module is designed for the passenger side of a vehicle, the container may be located just behind the vehicle dashboard, cosmetic cover, or passenger-side instrument panel (hereinafter referred to as "dashboard") and the cover may form an integral part of the vehicle dashboard.
When the vehicle is involved in a collision, a crash signal initiates operation of the inflator to cause the air bag to deploy. The inflator provides an inert gas (e.g., nitrogen) which is directed under pressure into the air bag to force the air bag out of the canister incorporated in the module and into the passenger compartment of the vehicle. As the air bag is forced out of the module, the pressure exerted on the driver-side protective cover or dashboard causes selected portions of the cosmetic cover to separate, in a predetermined manner, along tear seams or breakaway seams (hereinafter referred to as "tear seams") to enable the air bag to be directed into the passenger compartment.
In one of the conventional methods for mounting a passenger-side air bag cushion to a two-part canister, the base of the air bag cushion is wrapped over the bottom edge of the first or top canister section. The top canister section is inserted into the base section, thereby containing the air bag cushion between the two canister sections, and a diffuser is installed in the interior of the canister. The canister sections, air bag cushion, and diffuser are joined together by rivets.
In the event of a collision, the large forces produced by the inflation of the bag and the impact of the body of the occupant against the bag tend to pull the clamped portion of the bag from the canister mounting. The force holding the air bag to the upper retainer of the canister is not evenly distributed over the entire area of the abutment between the upper retainer section and the lower retainer section. Instead, the force of holding the air bag to the upper retainer of the canister is concentrated in the shearing resistance of that part of an air bag which has a width corresponding to the diameter of the fastener and a length corresponding to the distance from the fastener to the edge of the gas inlet opening of the air bag. This clamping action of the retainer section may be insufficient to prevent separation of the bag from the retainers. Such separation may permit the escape of gas directly into the passenger compartment of the vehicle. Further, the edge of the canister top section over which the air bag cushion is wrapped may act like a cutting blade during the deployment of the air bag cushion, thereby cutting the base of the air bag cushion. This may release the air bag cushion from the canister allowing gas to escape into the passenger compartment, thus the gas in not useable for the deployment of the air bag cushion.